FtpWebRequest Class: Creating Remote Directories

So a question that you are probably asking yourself is, if BizTalk 2006 Rx has a FTP adapter that ships out of the box, why am I concerning myself with this .Net Class? The reason why I am concerning myself with this is that if you need to ensure that a remote folder exists, before you write the file, you can use this class to execute FTP commands against a remote system.

My Requirements

I need to connect to a Unix file system and deliver 3 files: a "work" file, a "sig" file and an "archive" file. So if you had a static file structure, this is not a difficult feat. My issue is that the archive file needs to be placed in the current day's directory. The directory structure that I need to deliver to is /arch/yyyy/mm/dd.

The way the class behaves is that I cannot just assume that the parent folder exists. If I try to determine if 2008/01 exists, I will get an exception, but I won't be able to determine which folder does not exist. So based upon this, I need to ensure that the correct Year folder exists, then month and then day.

Solution Options

1. Write a Unix script that is included in a Crontab job that routinely checks for missing folders, when a missing folder is encountered, the script creates it.


2. As part of the BizTalk process, for each file that is about to be written, use the FtpWebRequest Class to check to see if the folder(s) exist. If they do not, then create them as required.


3. Much like Option #2, have BizTalk create the folder structures, but create a routine that runs once a day and creates folders out several days in advance.


4. Manually create the folders and "assume" they exist.

Solution Chosen

I chose Option #3 for a few reasons:

1. I come from a .Net background and am not all that anxious to get my hands dirty writing Unix scripts.


2. While Option #2, would work it would create unnessary connections to the Unix System during every archive file write. It wouldn't kill the performance, but is not ideal.


3. Option #3 runs once a day and I can schedule it so that it runs during off-peak load. I can use MOM to notify me of any exceptions that occur and use the SMTP adapter to send me a summary of the folders that were created successfully.
   

So what is the big fuss?

During the development of the solution, I ran into some interessing quirks about the FtpWebRequest Class. There is not a lot of documentation on it and there seems to be ample problems with it on the forums.

So to start with, familiarize your self with the MSDN documentation: http://msdn2.microsoft.com/en-us/library/system.net.ftpwebrequest.aspx

FtpWebRequest Class Behaviour

1. If you try to execute a directory listing on an empty folder, a
   System.Net.WebException will be raised. For instance if a person is looking for all folders in a directory called /2008 and there are no child folders in this folder, an exception will be raised. I find this behaviour to be extremely odd and I think this creats a lot of confusion for developers.


2. I have not found a way to 'defensively' code against scenario #1. The only way that I have been able to deal with this situation is to catch the exception and then create the new folder. I do realize that it is not best practice to use exception handlers as a way to deal with logic, but in this class I did not find a way around it.


3. If child folders to exist in the directory being listed, a stream is returned which can easily be assigned to a string. You then need to search the string to see if the folder already exists. Also note that in this list, you will find Carriage Return/Line Feed characters which are represented as \r\n


4. If your FTP Server has different file mounts and you need to navigate up the tree, you can use '%2E%2E' which is the equivalent of '..' So for instance when I log into my FTP server, I get logged into /home/'username'. The path to my archive directory is /'company'/'environment'/interfaces/'interface'/inbound/arch/ . So before I check to see if the archive folder exists, I want to go up two directories, before I navigate to it. '/home' is a sibling folder of '/company' The way this looks in code is:
   string ftpURI = "ftp://" + server + "/%2E%2E/%2E%2E" + path;

The Code

So my purpose for this code is to see if a target directory exists, if it does not exist, I want to create it. To simplify the code, I have removed determining if the Month and Day exist, but the concept remains the same. Ultimately, the return string is my entire archive path: /yyyy/MM/dd . If I encounter an exception that is unexpected ( something other than a System.Web.Exception) I throw an exception back to the caller.

Here is some sample code that can be called from .Net or BizTalk if you put it into a Serializable attributed class:

public string CreateNewUnixArchiveFolder(string path, string server, string username, string password, string currentYear, string currentMonth, string currentDay)

        {

            string tmpStr = "";

            FtpWebResponse FTPResp;
            FtpWebRequest request;
            Stream ftpRespStream;
            StreamReader sr;
            string folderList;
            string ftpURI = "ftp://" + server + "/%2E%2E/%2E%2E" + path;
            tmpStr = currentYear + currentMonth + currentDay;

            try
            {
                request = (FtpWebRequest)WebRequest.Create(ftpURI);
                request.KeepAlive = false;
                request.Method = WebRequestMethods.Ftp.ListDirectory;
                request.Credentials = new NetworkCredential(username, password);
                try
                {
                    FTPResp = (FtpWebResponse)request.GetResponse();
                    ftpRespStream = FTPResp.GetResponseStream();
                    sr = new StreamReader(ftpRespStream, Encoding.Default);
                    folderList = sr.ReadToEnd();
                    //close the objects
                    ftpRespStream.Close();
                    request = null;

                    //save the list into a string
                    if (!folderList.Contains(currentYear.Replace("/", "") + "\r\n"))
                    {   // Parent folder is not empty so no exception thrown, but current Year does not exist
                        //Current Year does not exist in archive...need to create it
                        request = (FtpWebRequest)WebRequest.Create(ftpURI + currentYear);
                        request.KeepAlive = false;
                        request.Method = WebRequestMethods.Ftp.MakeDirectory;
                        request.Credentials = new NetworkCredential(username, password);

                        FTPResp = (FtpWebResponse)request.GetResponse();
                        ftpRespStream = FTPResp.GetResponseStream();

                        //close the objects
                        request = null;
                        ftpRespStream.Close();
                    }
                }
                catch (System.Net.WebException)
                {
                    //Current Year does not exist in archive...need to create it
                    request = (FtpWebRequest)WebRequest.Create(ftpURI + currentYear);
                    request.KeepAlive = false;
                    request.Method = WebRequestMethods.Ftp.MakeDirectory;
                    request.Credentials = new NetworkCredential(username, password);
                    FTPResp = (FtpWebResponse)request.GetResponse();
                    ftpRespStream = FTPResp.GetResponseStream();

                    //close the objects
                    request = null;
                    ftpRespStream.Close();
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
            return tmpStr;
        }

 FtpWebRequest